FIG. 1 is a view showing the construction of a conventional surface-mount chip antenna 10.
As shown in FIG. 1, the conventional surface-mount chip antenna 10 includes a dielectric block 11 made of ceramic material or resin. The dielectric block 11 includes a ground electrode 14 formed on the first surface 12 thereof, a radiation electrode 19 formed on the second surface 13 thereof, and a feeding pattern 15 formed across a portion of one side of the dielectric block 11 from a portion of the first surface 12. The radiation electrode 19 is spaced apart from the feeding pattern 15 and is connected to the ground electrode 14 via two short circuit portions 16 and 17 that are respectively formed on two sides of the dielectric block 11. Furthermore, the radiation electrode 19 has a length of λ/4 at a resonance frequency.
The surface-mount chip antenna 10 described above forms a resonance circuit using capacitance existing between the ground electrode 14 and the radiation electrode 19 and the inductance of the radiation electrode 19, and adjusts the resonance frequency by coupling the radiation electrode 19 with the feeding pattern 15 using the capacitance existing between the feeding pattern 15 and the radiation electrode 19. However, there is a problem in that it is difficult to provide multi-frequency band communication service because an electrode appropriate to a specific resonance frequency is formed through a certain pattern-forming process and then only a single frequency band is used as a usable frequency band.
FIG. 2 is a view showing the construction of a conventional ceramic chip antenna.
As shown in FIG. 2, the conventional ceramic chip antenna 20 includes a chip main body 21 formed by stacking a plurality of green sheets, which are made of a ceramic dielectric material, a first helical conductor 22 formed in the chip main body 21 in a helical form, and a second helical conductor 23 disposed in parallel with the first helical conductor 22 in the chip main body 21 and formed in a helical form. The first helical conductor 22 is formed using a plurality of horizontal and vertical strip lines in a helical form, and the helical rotational axis A of the first helical conductor 22 is parallel to the bottom 24 and side surfaces 25 of the chip main body 21 made of ceramic. In the same manner, the second helical conductor 23 is formed using a plurality of horizontal and vertical strip lines in a helical form, and the helical rotational axis B of the second helical conductor 23 is parallel to the bottom 24 and side surfaces 25 of the chip main body 21.
In this case, the first helical conductor 22 and the second helical conductor 23 are independently formed without being connected to each other, the helical rotational axes A and B of the conductors 22 and 23 are parallel to each other, and the strip lines and via holes in the respective green sheets are three-dimensionally connected to each other through precise alignment so that the first and second helical conductors 22 and 23 are formed.
Furthermore, voltage supply terminals 26 are formed at respective ends of the helical conductors 22 and 23 so as to protrude outside the main body 21. In this case, if voltage is applied to the helical conductors 22 and 23 through the voltage supply terminals 26, a problem occurs in that the helical conductors 22 and 23 resonate in two different frequency bands, and thus it is difficult to provide multiple frequency band radio communication service.
Although the conventional ceramic chip antenna described above has recently been developed to the level at which it is possible to contain the antenna in a mobile terminal in the form of a small-sized chip, there are problems in that a ceramic material exhibiting a high permittivity is used, therefore the manufacturing cost of the antenna is high and the resonance frequency band thereof varies due to high-temperature sensitivity.
Current mobile communication terminal becomes small-sized and light-weighted and require the diverse service-providing function.
In order to satisfy above demand, the built-in circuit and the components adapted in mobile communication terminal become multi-functioned and at the same time small-sized.
Such trend is identically required to the antenna which is one of important components of the mobile communication terminal.
As antenna for mobile communication terminal used in general, a built-out helical antenna, planar antenna (MPA) of a built-in planar inverted F antenna (PIFA) and ceramic chip antenna are employed.
The helical antenna is used together with monopole antenna as built-out antenna fixed on upper part of the terminal.
In the form in which the helical antenna and the monopole antenna are used together, if the antenna is extracted from terminal main body, it operates as the monopole antenna, and if inserted, it operates as λ/4 helical antenna.
These antennas have advantage in that these get high gain but have disadvantage in that specific absorption rate (SAR) is not good due to non-directivity.
In other words, so as to overcome these problems, the MPA of the planar inverted F antenna (PIFA) having low profile structure or the ceramic chip antenna is provided.
The above MPA of PIFA type and ceramic chip antenna are built-in antenna. Since it is configured within inner part of the mobile communication terminal, the outward appearance of the mobile communication terminal can be designed finely and can be durable from external impact.
The above MPA of the PIFA type and the ceramic chip antenna are developed into dual band antenna form of the double radiator responsible for mutually different frequency band, that is high frequency band and low frequency band according to multi-function trend.
The performance of the above MPA is somewhat lower than that of the built-out antenna. But it has advantage in that it is embedded, so it has developed successively up to now. And it has disadvantage in that space insurance is not easy due to large size (35*20*6) and the structure must be changed whenever the mobile communication terminal is changed, and cost is high with respect to structure.
Further the ceramic chip antenna has small size and high efficiency. But it is disadvantage in that it is too sensitivity from external factor due to narrow bandwidth and the cost is high.